Abstract:

Given its large population, vigorous and water-intensive agricultural industry, and
important ecological resources, the western United States presents a valuable case study for
examining potential near-term changes in regional hydroclimate. Using a high-resolution,
hierarchical, five-member ensemble modeling experiment that includes a global climate
model (Community Climate System Model), a regional climate model (RegCM), and a
hydrological model (Variable Infiltration Capacity model), we find that increases in
greenhouse forcing over the next three decades result in an acceleration of decreases in
spring snowpack and a transition to a substantially more liquid-dominated water resources
regime. These hydroclimatic changes are associated with increases in cold-season days
above freezing and decreases in the cold-season snow-to-precipitation ratio. The changes in
the temperature and precipitation regime in turn result in shifts toward earlier snowmelt,
base flow, and runoff dates throughout the region, as well as reduced annual and warm-season
snowmelt and runoff. The simulated hydrologic response is dominated by changes in
temperature, with the ensemble members exhibiting varying trends in cold-season
precipitation over the next three decades but consistent negative trends in cold-season freeze
days, cold-season snow-to-precipitation ratio, and 1 April snow water equivalent. Given the
observed impacts of recent trends in snowpack and snowmelt runoff, the projected
acceleration of hydroclimatic change in the western U.S. has important implications for the
availability of water for agriculture, hydropower, and human consumption, as well as for the
risk of wildfire, forest die-off, and loss of riparian habitat.

Description:

This is the publisher’s final pdf. The published article is copyrighted by the American Geophysical Union and can be found at: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)2169-8996.